Fabrication of a high-power pump and signal combiner with an asymmetric tapered fiber bundle utilizing un-pretreated pump fibers

We report a fabrication method for addressing the non-uniform arrangement issues associated with the asymmetric tapered fiber bundles (TFBs) in high-power pump and signal combiners (PSCs), which do not require pre-treatment of the pump fibers. It employs a homemade thin-walled glass tube with the coating layer, and six pump fibers surround it evenly to collectively form the TFB, while the signal fiber remains unaffected during the tapering process of the fiber bundle. The 3D simulation model of the backward (6 + 1)×1 PSC was established by the refractive index distribution method to calculate the transmission efficiency of the pump light and signal light, and then identify the optimal preparation parameters for achieving the best efficiency. In this model, a simulated quasi-uniform energy distribution light field was used as the input of the pump fiber, which can optimize the previous calculation method. Experimental results exhibited that the backward (6 + 1)×1 PSC achieved signal light and pump light transmission efficiencies of over 96% and 98%, respectively, the beam quality degradation is ΔM²= 0.09, and the total output pump power was 4.102 kW. The experimental results are in good agreement with the simulation results.